Reality star Ramona Singer turned into a real-life hero when she helped a pal track down a nanny who allegedly stole thousands of dollars in jewelry from her Park Avenue apartment.

Composer and philanthropist Lucia Hwong Gordon went on vacation with her kids last month and realized upon her return that precious gems — including a diamond-and-ruby necklace — as well as her kids’ baptismal jewelry and “family heirloom silver,” among other items, were missing, sources said.

Gordon asked live-in nanny Raquel Santos, who was hired through a staffing agency, if she’d seen the pricey possessions — and Santos “started crying,” said a source, then allegedly handed over slips to a pawn shop.

A complaint filed with the Manhattan DA’s office alleges Santos then took Gordon to two pawn shops where some of the possessions were on display. But the socialite didn’t report Santos, even when she realized more items were missing. She asked friends, including Singer, for advice.

“Lucia was distraught,” a source said. “She didn’t want to file any charges. It was traumatic.”

But “Ramona said she needed to speak up before the woman victimized another family,” our source said. The “Real Housewives” star told Gordon, “‘I’m doing a Ramona on you! You’re going to report this woman.”

The cops were called, and Singer advised Gordon to call the nanny to say she wanted to buy back the rest of her belongings. When Santos arrived at the Park Avenue home, she allegedly had more of Gordon’s goods and was arrested.

Singer told us: “I’m thrilled justice was served. My friend showed strength and perseverance. It was important that this was investigated. If it had not been investigated, she might have just gone to work for another family and done the same thing.”

Gordon had no comment, but a friend said, “Ramona gave her the strength to deal with this.”

Santos’ lawyer said, “The DA and I are endeavoring to resolve this matter. We expect the victim will not have lost any of her property.”